1. Field of the Invention
The present invention relates to a protective device for a turbo molecular pump and a method of protecting a turbo molecular pump, and to, for example, a protective device for a turbo molecular pump and a method of protecting a turbo molecular pump when an abnormal phenomenon such as injection of atmospheric air to the turbo molecular pump during the operation occurs.
2. Description of the Related Art
A turbo molecular pump is mounted in, for example, a vacuum tank (chamber) of a semiconductor manufacturing apparatus and is used to discharge process gas within the vacuum tank or used in the case where a high vacuum condition is realized like evacuating a chamber in which an observation sample of an electronic microscope is installed.
In some cases, the interior of the vacuum tank is rapidly exposed in the atmospheric pressure like a case where a leak valve of the vacuum tank is erroneously opened by the operator during the operation of the turbo molecular pump or a measurement equipment or an observation window mounted on a vacuum portion is broken down.
In the interior of the turbo molecular pump, rotor blades are rotated at a high speed of, for example, about 30,000 rpm together with a rotor. For this reason, when such atmospheric air is introduced into the turbo molecular pump that works under such a high vacuum condition, there is a fear that a load the turbo molecular pump receives is rapidly increased and constituents such as a bearing or rotor blades constituting the turbo molecular pump or a joint portion of the constituents would be damaged.
In order to protect the turbo molecular pump when such an abnormal phenomenon occurs, in the conventional turbo molecular pump, the abnormal phenomenon is detected as in a case where, for instance, a vibration of the rotor in a radial direction or a thrust direction is detected or a change in rpm of the rotor is detected and a protective device like stopping the turbo molecular pump is provided.
However, the kinds of the abnormal phenomena against which the turbo molecular pump should be protected are various like an occurrence of a damage of bearing portion, an entrainment of a foreign matter into the pump interior, a damage of revolving bodies such as rotor blades or the like, an external turbulence such as an earthquake, a power shortage or the like in addition to the above-described accidental injection of the atmospheric air.
However, when the abnormal phenomenon occurs, the conventional protective device for the turbo molecular pump does not well cope with the abnormal phenomena according to the kind thereof.
Accordingly, an object of the present invention is to provide a protective device for a turbo molecular pump and a method of protecting a turbo molecular pump that may cope with abnormality according to the kind thereof when the abnormal phenomenon occurs.
In order to achieve the above-mentioned object, according to the present invention, there is provided a protective device for a turbo molecular pump having a rotor for undergoing rotation, an intake port for sucking gas by rotation of the rotor, and an exhaust port for exhausting the gas sucked from the intake port. The protective device comprises detecting means for detecting that an abnormal phenomenon occurs in the turbo molecular pump, abnormal phenomenon inference means for inferring a type of the abnormal phenomenon detected by the detecting means, value obtaining means for inferring a magnitude of damage given to the turbo molecular pump by the abnormal phenomenon inferred by the abnormal phenomenon inference means and obtaining a value weighted based on the inferred magnitude of the damage, value accumulation means for accumulating the value obtained by the value obtaining means, sum obtaining means for obtaining a sum of the values accumulated in the value accumulation means, and protecting means for protecting the tubo molecular pump in the case where the sum obtained by the sum obtaining means exceeds a predetermined value (first structure).
In the first structure of the present invention, there may be constructed a protective device further comprising a change rate obtaining means for obtaining a change rate in a rotating speed of the rotor, in which the abnormal phenomenon inference means infers a kind of the abnormal phenomenon from a change rate in rpm of the rotor obtained by the change rate obtaining means (second structure).
Also, in the first structure of the present invention, there may be constructed a protective device, further comprising a load detecting means for detecting a load to be applied to the rotor in an axial direction of the rotor, in which the abnormal phenomenon inference means infers a kind of the abnormal phenomenon from a load detected by the load detecting means (third structure).
Further, in any one of the first to third structures of the present invention, there may be constructed a protective device, further comprising an rpm obtaining means for obtaining an rpm of the rotor, in which the value obtaining means infers a magnitude of the damage according to the rotating speed of the rotor obtained at least by the rpm obtaining means when the abnormal phenomenon is detected by the detecting means (fourth structure).
Further, in any one of the first to fourth structures of the present invention, there may be constructed a protective device, in which the protective means is provided with at least one of a stopping means for stopping the turbo molecular pump, a restart disabling means for disabling a restart instruction for restarting the turbo molecular pump, and an alarm means for giving an alarm to an operator of the turbo molecular pump (fifth structure).
Further, in any one of the first to fifth structures of the present invention, there may be constructed a protective device, in which the abnormal phenomenon inferred by the abnormal phenomenon inference means is the fact that the atmospheric air is injected from the intake port during the operation of the turbo molecular pump.
Further, there may be constructed a protective device, in which a kind of the abnormal phenomenon inferred by the abnormal phenomenon inference means includes, in addition to the injection of the atmospheric air, at least one of a touchdown of the rotor to a protective bearing for protecting the rotor in the case where the rotor is held by a magnetic bearing, a mixture of foreign matters to the bearing for holding the rotor, a power outage of a power to be fed to the turbo molecular pump, and an external turbulence of the turbo molecular pump by an external force.
In another aspect, in order to achieve the above-mentioned object, there is provided a method of protecting a turbo molecular pump according to the present invention. A turbo molecular pump having a rotor for undergoing rotation, an intake port for sucking gas by rotation of the rotor, and an exhaust port for exhausting the gas sucked from the intake port is provided. A fact that an abnormal phenomenon is generated in the turbo molecular pump is then detected and a type of the abnormal phenomenon is inferred. A magnitude of damage given to the turbo molecular pump by the inferred abnormal phenomenon is then inferred and a value weighted based on the inferred magnitude of the damage is obtained. The value obtained based on the inferred magnitude of the damage is then accumulated. A sum of the accumulated values is then obtained. A protecting means for protecting the turbo molecular pump is then operated in a case where the sum of the accumulated values obtained exceeds a predetermined value.